1. Field of the Invention
This invention relates to a slide rheostat type linear characteristic sensor that has a substrate and a resistor formed thereon and contacted with a brush. It relates particularly to a slide rheostat type linear characteristic sensor which is applicable to a potentiometer, a throttle position sensor, an encoder and the like.
2. Description of the Related Art
FIG. 8 is a front view showing main parts of a conventional slide rheostat type linear characteristic sensor.
As illustrated in FIG. 8, the prior art sensor has a circuit board composed of a substrate 31 and a fixed resistivity of resistor 32 formed on the substrate 31 by sintering. A conductor brush 33 is so arranged that it touches the resistor 32 at a predetermined contact pressure and slides thereon. A terminal 35 and a terminal 36 are provided on opposite ends of the resistor 32. The terminals 35 and 36 are electrode terminals that apply a prescribed voltage to the resistor 32. The brush 33 conducts a contact potential relative to the resistor 32 to the terminal 37, from the voltage applied between the terminals 35 and 36 via a fixed conductor 34. The contact potential of the brush 33 is outputted from a terminal 37. A not shown harness is connected with the terminals 35, 36 and 37. Thus, the contact potential is varied linearly according to a contact position of the brush 33 and the resistor 32.
In recent years, such sensor was widely used for a variety of detecting systems such as a G sensor and a height sensor. There is a request for such measures as generating a clamping current in order to distinguish a normal state from an abnormal state like a breaking of the harness and a short-circuit.
However, the above mentioned sensor has no clear or definite clamping resistance even if used as the throttle position sensor. Therefore, there is a possibility that the throttle position sensor sometimes outputs a zero volt, or Vcc (supply voltage) even when it is used normally. As such throttle position sensor possibly outputs the zero volt or Vcc even in case of breaking of the sensor (Vcc) or a short circuit of the sensor (0V), a computer cannot judge whether the sensor is in order or out of order. As a result, there is a fear that a fail-safe does not work properly.
There may be an idea that a clamping resistor is assembled as a separate member so as to output a clamping voltage. In this case, there is a fear that costs for such parts will substantially increase production costs. Another problem is that, if the clamping resistor is disposed merely on another place than a place of a detecting resistor, an accurate detection is impossible due to influences of an atmosphere temperature where the sensor is positioned. In case the clamping resistor is connected to the detection resistor to be one successive resistor, an adjusting device is necessary in attaching the sensor in order to lessen an output voltage change due to assembling errors, thereby increasing costs.